picture of the day

Diagram showing the four elements, seasons and
body types, based on an edition of Isidore of
Seville’s Liber de Responsione Mundi (6th
or 7th century CE), Augsburg in 1472. Courtesy
Huntington Library.

Elementary Knowledge
May 31, 2010

A cornerstone of ancient Greek
science was the theory of the four
elements: Pythagoreans, Platonists,
Aristotelians and Stoics alike
subscribed to the idea that all
visible matter is formed of earth,
water, air and fire, varying only in
concentration and mode of
intermixture.

The 'four
element theory' reached its standard
form when Empedocles of Acragas
(±492-432 BCE) synthesised earlier
attempts to identify the prima
materia, the primary or original
substance from which all else was
derived – historically as well as
chemically.

During the formative period of Greek
philosophy, Thales of Miletus
(±624-547 BC) had argued that “the
beginning and end of the universe
was water”, while the Pythagorean
Hippasus of Metapontum (±500 BCE),
Heraclitus of Ephesus (±535-475 BCE)
and Zeno of Elea (±490-±430 BCE?)
all recognised fire as the first
principle. Other opinions were
voiced as well.

The notion of the four classical
elements remained intact for
centuries and was used to account
for commonly observed physical
processes, including weather and
climate, as well as for cosmogonic
theories. The only significant
modification was Aristotle’s
treatment of the ‘fire’ constituting
stars and planets as a separate,
fifth element called ‘aether’,
an innovation which only the
Aristotelians seem to have embraced.
As one follower put it: “The
substance of the heaven and the
stars we call aether … it is an
element different from the four
elements, pure and divine.” The idea
was that aethereal objects were
perfectly immutable, while ‘fiery’
ones were prone to change and decay.

The theory fell out of favour with
the rise of modern chemistry in the
late 17th century. In 1669, the
German physician and alchemist,
Johann Joachim Becher, split the
element of earth into three,
corresponding to different degrees
of viscosity and fluidity. During
the same decade, the Irish
alchemist, Robert Boyle, while
pioneering chemical analysis,
theorised that the traditional
elements really were compounds and
mixtures, consisting of smaller
particles with a greater diversity.

As the infant science of chemistry
progressed, the number of recognised
elements rose from 33 in 1789 and 49
in 1818 to the 66 that Dmitri
Mendeleyev incorporated in his
periodic table in 1869. This further
increased to the 118 elements that
have been observed up until now,
either in the laboratory, in space
or in nature.

From this point of view, the ancient
Greek notion of ‘four elements’
sounds hopelessly obsolete, but is
it reasonable to view it as a
precursor to the modern chemical
definition of ‘elements’? Are
ancient and modern ‘elements’ really
the same thing? It is true that
Platonists associated each of the
four elements with one of the
regular polyhedra, so as to make
sense of their physical properties.
But were these philosophers really
so naïve as to imagine that all
known physical behaviour is
reducible to just four constituents?

A recurrent topic in the classical
literature concerned the cycles
according to which one ‘element’
would transform into another. In the
modern sense of the word, elements
jumping positions in the periodic
table must be understood either in
terms of alchemy or of nuclear
chemistry, such as radioactive decay
or nuclear fusion. Yet it is clear
that this is not what Greek
philosophers were preoccupied with.
Heraclitus, for example, “called
change the upward and the downward
path, and held that the world comes
into being in virtue of this.

When fire is condensed, it becomes
moist, and when compressed it turns
to water, water being congealed thus
turns to earth, and this he calls
the downward path. And, again, the
earth is in turn liquefied, and from
it water arises, and from that
everything else; for he refers
almost everything to the evaporation
from the sea. This is the path
upwards”. Clearly, speculations of
this type do not involve chemical
elements, but states of
aggregation.

After the English natural
philosopher, Joseph Priestley
(1733-1804), successfully isolated
different ‘airs’ or gases, including
oxygen, three states of matter were
widely recognised – solids, liquids,
and gases. At a later date, one of
the most significant fall-outs of
the study of electromagnetism was
the recognition of a fourth state.
Its discoverer, the English
scientist, Michael Faraday
(1791-1867), dubbed it “radiant
matter”:

“If now we conceive a change as far
beyond vaporisation as that is above
fluidity, and then take into account
also the proportional increased
extent of alteration as the changes
rise, we shall perhaps, if we can
form any conception at all, not fall
far short of radiant matter … The
simplicity of such a system is
singularly beautiful, the idea
grand, and worthy of Newton’s
approbation.”

Sixty years later, it was Faraday’s
compatriot, Sir William Crookes
(1832-1919), who followed up in
earnest the suggestion of “Matter
classed into four states – solid,
liquid, gaseous, and radiant – which
depend upon differences in the
essential properties”. The term
plasma was employed for the
“radiant” or partly ionised gases by
the Nobel-prize winning American
chemist and physicist, Irving
Langmuir (1861-1957), in 1928.

The discovery of the plasma state
allows a reappraisal of the ancient
theory of elements. If the four
‘elements’ of the Greeks were really
states of matter, the concept is no
longer antiquated, but up to speed
with current understanding. If
‘earth’ corresponds to solids,
‘water’ to liquids, ‘air’ to gases,
and ‘fire’ to plasmas, the likes of
Empedocles effectively anticipated
Faraday by more than two millennia
with their insight that fire and
lightning represent an essentially
different regime of matter than
ordinary ‘air’. Faraday himself was
acutely aware of this connection:
“It was what the ancients believed,
and it may be what a future race
will realise.”

With remarkable prescience, Crookes,
too, foresaw the immense scientific
potential of the ‘radiant’ state as
early as 1879:

“In studying this Fourth state of
Matter we seem at length to have
within our grasp and obedient to our
control the little indivisible
particles which with good warrant
are supposed to constitute the
physical basis of the universe. … We
have actually touched the border
land where Matter and Force seem to
merge into one another, the shadowy
realm between Known and Unknown
which for me has always had peculiar
temptations. I venture to think that
the greatest scientific problems of
the future will find their solution
in this Border Land, and even beyond
…”

Those at the forefront of plasma
science today would agree that
plasma constitutes “the physical
basis of the universe” and that it
can potentially solve “the greatest
scientific problems”. Indeed, owing
to its ubiquity in space, plasma has
been promoted from being the
‘fourth’ state to the fundamental
state of matter. And this, again,
accords quite well with Heraclitus’
hoary adage: Tà dè pánta oiakízei
keraunós – ‘Thunderbolt steers
all things’.

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